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From: gwyn@brl-tgr.ARPA (Doug Gwyn <gwyn>)
Newsgroups: net.unix-wizards
Subject: Re: TAR DOES NOT SWAP BYTES
Message-ID: <1753@brl-tgr.ARPA>
Date: Thu, 26-Sep-85 18:20:26 EDT
Article-I.D.: brl-tgr.1753
Posted: Thu Sep 26 18:20:26 1985
Date-Received: Sat, 28-Sep-85 08:19:35 EDT
References: <235@thunder.UUCP> <604@neuro1.UUCP> <2818@sun.uucp>
Organization: Ballistic Research Lab
Lines: 19

> There are known cases of brain-damaged *hardware* swapping bytes.  The case
> I know of is a big-endian Multibus machine with an extremely stupidly
> designed tape controller.  If you write a tape on this machine, and want to
> read it in on a sane machine, you have to stick "dd" in front of the "tar"
> (or "cpio" or whatever).
> 
> The rule for correctness of byte order in a tape controller is simple.  If
> you have the string "Now is the time for all good parties to come to the aid
> of man" in memory, and tell the tape controller to write this to a tape, the
> first byte in the block should be a capital "n", followed by a lower-case
> "o", followed by a lower-case "w", followed by a blank, etc..  Violate this
> and you'll force everybody who didn't violate this to swap bytes when
> reading your tapes.

Yup, I believe IBM started this byte-swapping magtape foolishness
because of some bogus idea about big-endian byte order being "more
natural" on some 16-bit machine they had.  Some magtape controllers/
interfaces have jumpers to allow them to be operated in either normal
or swabbed mode.


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